1. Field of the Invention
The present invention relates to providing protection units to metallic interface units in a telephone system. In particular, the present invention relates to providing protection units without a dedicated protection switch and, at the same time, allowing metallic interface units of various service levels.
2. Discussion of the Related Art
In a digital telephone system, a xe2x80x9cmetallicxe2x80x9d interface is an interface through which the copper wires of the subscriber equipment arrive at an entry point to the system. Conventionally, the metallic interface is characterized by a pair of xe2x80x9ctip/ringxe2x80x9d wires. The signals in the tip/ring wires may represent voice, data traffic or both. To maximize availability of the system, one or more stand-by interfaces (xe2x80x9cprotection unitsxe2x80x9d) are typically provided, so that, when a primary metallic interface (xe2x80x9cworking unitxe2x80x9d) fails, the tip/ring signals of the working unit can be re-routed to the protection unit without the subscriber suffering an undesirable disruption of service.
In the prior art, one of two types of methods for providing protection units is typically used. In the first method, a dedicated switching equipment (xe2x80x9cprotection switchxe2x80x9d) is used. The typical protection switch has an array of relays that are used for switching the signals from a failed working unit to an available protection unit. The protection switch approach provides satisfactory performance in multiplexed products for trunk (i.e. interoffice) operations, where the number of types of metallic interfaces are relatively small. The protection switch approach, however, becomes inadequate in systems where subscriber traffic of many different levels of service (e.g. DS1, DS2, voice frequency channel units) are multiplexed. Different levels of service have different protection requirements. For example, since a DS-2 interface has a much wider bandwidth than a DS-1 interface, the potential for a more significant data loss is higher in the DS-2 interface than the DS-1 interface, so that a higher protection requirement for the DS-2 interface is likely needed. In these systems, however, the protection switch approach dictates an expensive and complex switching control structure to ensure that the signals in a failed working unit is properly switched to a protection unit of the appropriate type.
The second type of methods for providing protection units involves a protection bus. Under this approach, a failed working unit routes, through its relays, the signals on the tip/ring wires to the protection bus. The control circuit then activates a protection unit to connect its input terminals to the protect bus to receive the re-routed tip/ring signals. This protection bus approach, while eliminating the complex protection switch, requires that the failed working unit remain capable of making a connection for routing the subscriber signals to the protection bus. In addition, the subscriber""s service is necessarily interrupted when the failed unit is removed for repair or replacement.
According to the present invention, a system and a general method provide protection for metallic interfaces of different service levels. Under the present invention, a metallic interface unit is assigned a partner unit which switches the metallic interface unit""s tip/ring input signals to a protection bus when a failure occurs in the metallic interface unit. A stand-by unit (xe2x80x9cprotection unitxe2x80x9d) then receives the re-routed tip/ring signals from the protection bus. Since the partner unit performs only a signal re-routing function, expensive protection switch units need not be provided. In addition, full protection can be provided because the failed working unit is not required to switch its own input tip/ring signals to the protection unit.
In one embodiment of the present invention, the metallic interface system includes (i) a protection bus; (ii) metallic interface units each having (a) input terminals for receiving a first set of tip/ring signals, (b) input terminals for receiving a second set of tip/ring signals, (c) a processing circuit providing a metallic interface for the first set of tip/ring signals, and (d) a switch circuit coupled to the first input terminals and the second input terminals for coupling the first set of tip/ring signals to the processing circuit and for coupling, upon receiving an asserted control signal, the second set of tip/ring signals to the bus; and (iii) a protection metallic interface unit coupled to receive from the protection bus a set of tip/ring signals. In this metallic interface system, the protection metallic interface unit implements a metallic interface for the set of tip/ring signals it receives from the protection bus.
In the above embodiment, the present invention assigns a partner unit to a selected metallic interface. This partner unit is typically another metallic interface unit. In that embodiment, the partner unit is coupled to receive the first set of tip/ring signals of the selected metallic interface unit at its second input terminals. According to the present invention, since the partner unit merely re-routes the selected metallic interface unit""s tip/ring signals to the protection bus, the switch mechanism in each metallic interface unit can be the same, even though the partner unit and the selected metallic interface unit can be metallic interface units providing very different service levels. One significant advantage of the present invention is the possibility that metallic interface units of different types can coexist on the same shelf, sharing the same protection scheme. To simplify control, the selected metallic interface unit and the partner unit can be made to locate at adjacent slots on the same shelf.
According to another aspect of the present invention, the partner unit can include a control circuit providing a second control signal, which is used to disconnect the processing circuit of the failed metallic interface unit from its input ring/tip signals.
According to another aspect of the present invention, if the number of working units is odd, a selected metallic interface unit is assigned a protection unit as its partner. In one embodiment, protection relays in the selected metallic interface unit is used to couple a set of tip/ring signals from the protection bus to the protection unit. Under the present invention, the number of protection relays required grows linearly with the number of metallic interface units.
According to another aspect of the present invention the protection bus of a shelf can be segmented to allow the different segments of the protection bus to provide protection to metallic interface units of different service levels, or to provide a lower protection ratio for high speed applications.